13.9.1: Review Questions

Review Questions

Multiple Choice

1. Which IoT protocol uses a publish-subscribe model over TCP with three QoS levels and is the most widely used for IoT telemetry?
   • a) HTTP
   • b) CoAP
   • c) MQTT
   • d) AMQP
2. What is the primary advantage of edge computing compared to processing all IoT data in the cloud?
   • a) Lower hardware costs
   • b) Reduced latency and bandwidth by processing data near the source
   • c) Simplified security management
   • d) Elimination of the need for cloud services
3. An AWS IoT Core "Device Shadow" is best described as:
   • a) A backup copy of device firmware stored in S3
   • b) A cloud-based JSON document representing a device's desired and reported state
   • c) An encryption certificate for device authentication
   • d) A virtual machine running a simulation of the device

Short Answer

4. Compare MQTT and CoAP across four dimensions: transport protocol, communication model, overhead/efficiency, and ideal use case. When would you choose CoAP over MQTT?
5. Describe the four layers of a typical IoT-cloud architecture (device, network, processing, application). Give an example of a technology or service at each layer for a smart building monitoring system.
6. What is a device twin (or device shadow), and why is it important for managing devices that may be intermittently connected? Describe a practical scenario where the device twin pattern solves a real problem.
7. Explain three key security challenges unique to IoT deployments that do not apply to traditional cloud applications. For each challenge, describe a mitigation strategy.

True/False

8. True or False: MQTT runs over UDP, which makes it faster but less reliable than HTTP-based IoT protocols.
9. True or False: AWS IoT Core can automatically scale to support over a billion device connections.
10. True or False: Edge computing eliminates the need for cloud infrastructure — all processing happens on the edge device.

Answer Key:

1. c
2. b
3. b
4. MQTT: TCP, pub/sub, lightweight binary framing, ideal for persistent connections/telemetry streaming. CoAP: UDP, request/response (REST-like), very low overhead, ideal for battery-powered sensors that wake-send-sleep. Choose CoAP for extremely constrained devices on lossy networks needing REST semantics.
5. Device layer: sensors (temperature, humidity, occupancy). Network layer: Wi-Fi/Zigbee to IoT gateway, then to internet. Processing layer: AWS IoT Core (ingestion) + Lambda (processing) or edge compute for real-time alerts. Application layer: dashboard showing building conditions, automated HVAC control.
6. Device twin is a cloud JSON doc with "desired" and "reported" states. When a device is offline, the cloud app sets the "desired" state; when the device reconnects, it reads the desired state and acts. Example: A smart irrigation system in a rural area with intermittent connectivity — the farmer sets "water for 30 minutes" via the cloud app; the device gets the command next time it connects.
7. (1) Physical access — devices deployed in exposed locations can be physically tampered (mitigation: secure boot, hardware encryption). (2) Constrained resources — devices may lack compute power for strong encryption (mitigation: lightweight protocols like DTLS, hardware security modules). (3) Scale — millions of devices to manage credentials for (mitigation: certificate-based auth, zero-touch provisioning, automated rotation).
8. False (MQTT runs over TCP)
9. True
10. False